This invention relates generally to thin film electronic display or imager devices and more particularly to repair line structures contained in devices such as solid state radiation imagers having a matrix of electrically conductive address lines for controlling the active components of the device.
Address lines for conducting electrical signals to and from active components in a display or imager device are formed as integral parts of the structure of solid state imagers. These address lines usually form a matrix, with lines running in one direction designated as scan lines and lines disposed in a substantially perpendicular direction designated as data lines. Electrical signals (e.g. the voltage) on a scan line typically control a switching device, such as a field effect transistor (FET, also referred to as a thin film transistor, or TFT), that in turn couples the active component, such as a photosensor, to the data line so that an electrical signal from the photosensor (corresponding to the number of detected photons incident on the array) can be read out. The resultant signals are then used to electronically reproduce an image of the photons detected by the array of photosensors. In a display device comprising, for example, an array of liquid crystal display devices (LCDs), a similar address line structure is used.
A defect on a scan or data line can adversely affect overall performance of the thin film imager device. For example, an open circuit condition can disable active components connected to the address line beyond the point where the open circuit exists. A short circuit between a data and a scan line can also lead to inaccurate signals being applied to switching transistors connected to either of the shorted data or scan lines. In either case, multiple pixels in the device can be affected, thereby significantly diminishing its resolution. A device having defective address lines may have to be discarded, depending upon the degradation of the resolution of the display device resulting from the inoperative pixels resulting.
Given the expense of fabricating thin film electronic imager devices, it is desirable to have devices that are repairable at various points in the repair process. In one approach, a thin film display device has several auxiliary conductive lines disposed across the transmission lines on the sides of the device, usually outside the active areas of the device. See, e.g., U.S. Pat. No. 4,688,896, assigned to the assignee of the present invention, and which is incorporated herein by reference. In the display device described in that patent, bypassing an open circuit in a defective address line requires that one auxiliary (or repair) line be connected to the defective line at one side of the device (such as by laser welding the two lines together at a point where the lines cross over one another) and that a second auxiliary line be connected to the defective line on the other side of the device. The auxiliary lines are electrically connected by a jumper or the like, allowing the signal to be applied to the defective line on both sides of the open circuit condition.
These auxiliary (or repair) lines are typically formed as a part of the the fabrication process of the photosensor array, which includes the formation of address lines for the photosensor array and the photosensors. The repair lines are typically disposed along the edges of the array oriented perpendicularly to the address lines that extend from the array towards that edge of the array so that the repair lines are disposed in vertical alignment with a portion of respective address lines at crossover regions. The repair lines are typically electrically insulated from the address lines by dielectric material used in the fabrication of the FETs.
The conductive line and dielectric material covering it disposed on top of the crossover region is susceptible to damage in the processing steps that follow the deposition of the upper conductive lines, such as the deposition and patterning of the following components: TFT passivation layer, photodiode island, photodiode dielectric, common electrode, and barrier layer. The etching steps in this processing can result in the repair line being cut at the repair crossover, thereby rendering the repair line ineffective for use with the underlying address line, and, dependent on where the break in the repair line occurs, the entire repair line may be rendered nonfunctional. In particular, the edges of the repair line are most prone to damage during these processing steps.
As imager devices become larger, with increased numbers of scan and data lines, and as higher resolution is required of the device as a whole, fewer inoperative pixels can be tolerated. It is desirable that an imager assembly have multiple repair lines available that can be readily welded to a defective address line to effect a repair.
It is accordingly an object of this invention to provide a thin film electronic imager device structure having repair crossovers that are resistant to damage from device fabrication processes.
It is another object of the present invention to provide a durable thin film electronic device repair structure that readily provides for repair of the device.